Diagnostic testing of complex digital equipment is quite conventional. Typically, this involves the utilization of a global bus which services data distribution for the system as well as transmission of diagnostic data from system points to a CPU. The digital signals at test points are analyzed by the CPU; and when deviations are detected, the error-producing checkpoint may be found.
Although conventional diagnostic systems are capable of locating problem test points, they do require that the global bus of a digital system and the CPU be tied up for a period of time necessary to run diagnostic routines. Of course, this detracts from the data processing speed of the system.
Further, if the bus or CPU becomes temporarily inoperative, diagnostic testing of test points cannot be accomplished.